1. Field of the Invention
The invention relates to mechanical fasteners. More particularly, the invention relates to mechanical fasteners suitable for suspending fixtures such as acoustic tile ceilings, pipes, lighting fixtures, electrical cables, HVAC equipment etc.
2. State of the Art
Current practice in the construction trade and building industry is to suspend fixtures with wires which are fastened to a wall or ceiling. An example of a state of the art apparatus for suspending fixtures is illustrated in prior art FIG. 1. The apparatus generally includes an angle bracket 10 having two holes 12, 14, a fastener 16 (typically a nail or a screw), and a length of wire 18 (often six to eight feet long). The method for using the apparatus includes attaching the wire 18 through one of the holes 14, inserting the fastener 16 through the other hole 12, and fastening the fastener 16 to a wall or ceiling 20. An exemplary bracket and fastener are illustrated in U.S. Pat. No. 5,178,503 and U.S. Pat. No. 4,736,923.
The apparatus shown in FIG. 1 is often used to suspend fixtures from cement, stone, or other masonry material ceilings, typically in commercial buildings. The wires 18 are attached to ceiling tile grids, pipe brackets, HVAC ducts, lighting fixtures, etc. Because a relatively large variety of equipment is hidden above a suspended acoustic tile ceiling in a commercial building, the wires 18 are often six to eight feet long.
The fastener 16 is usually pre-fit into the hole 12 of the bracket 10 during manufacture. However, the wire 18 (usually 12 gauge galvanized steel) must be manually attached to the bracket 10 by inserting a free end of the wire through the hole 14, looping the wire onto itself and twisting it as shown in FIG. 1. This is often done by hand with a pair of pliers or may be done with the aid of a hand operated (or drill operated) crank such as the “wire tying fixture”, item number 00052075, sold by Hilti, Inc., Tulsa, Okla. These methods of attaching the wire to the bracket present several disadvantages.
The most apparent disadvantage is the cost of labor for the labor intensive task of twisting the wire. In order to be reasonably secure and satisfy some municipal codes, approximately eight inches of the wire must be twisted eight to ten turns about itself. In practice, many workers only twist the wire three or four times about itself. Still, the work is time consuming. The best productivity is not much more than about 300 pieces per hour and after about 500 pieces the worker needs to rest.
Another disadvantage is that this method of connecting the wire to the bracket is not very secure. Under a stress of about 50 lbs., the wire loop stretches and under a stress of about 210 lbs. the wire untwists.
Still another disadvantage is that the connection between the wire and the bracket is loose. Under normal circumstances, gravity provides tension between the wire and the bracket. However, in the case of an earthquake or a fire, the loose connection between the wire and the bracket allows vibration and movement of the fixtures supported by the wire. This can result in fixtures falling onto emergency workers and other similar hazards.